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/********************* */
/*! \file infer_info.h
** \verbatim
** Top contributors (to current version):
** Andrew Reynolds
** This file is part of the CVC4 project.
** Copyright (c) 2009-2019 by the authors listed in the file AUTHORS
** in the top-level source directory) and their institutional affiliations.
** All rights reserved. See the file COPYING in the top-level source
** directory for licensing information.\endverbatim
**
** \brief Inference information utility
**/
#include "cvc4_private.h"
#ifndef CVC4__THEORY__STRINGS__INFER_INFO_H
#define CVC4__THEORY__STRINGS__INFER_INFO_H
#include <map>
#include <vector>
#include "expr/node.h"
namespace CVC4 {
namespace theory {
namespace strings {
/** Types of inferences used in the procedure
*
* These are variants of the inference rules in Figures 3-5 of Liang et al.
* "A DPLL(T) Solver for a Theory of Strings and Regular Expressions", CAV 2014.
*/
enum Inference
{
INFER_NONE = 0,
// infer empty, for example:
// (~) x = ""
// This is inferred when we encounter an x such that x = "" rewrites to a
// constant. This inference is used for instance when we otherwise would have
// split on the emptiness of x but the rewriter tells us the emptiness of x
// can be inferred.
INFER_INFER_EMP = 1,
// string split constant propagation, for example:
// x = y, x = "abc", y = y1 ++ "b" ++ y2
// implies y1 = "a" ++ y1'
INFER_SSPLIT_CST_PROP,
// string split variable propagation, for example:
// x = y, x = x1 ++ x2, y = y1 ++ y2, len( x1 ) >= len( y1 )
// implies x1 = y1 ++ x1'
// This is inspired by Zheng et al CAV 2015.
INFER_SSPLIT_VAR_PROP,
// length split, for example:
// len( x1 ) = len( y1 ) V len( x1 ) != len( y1 )
// This is inferred when e.g. x = y, x = x1 ++ x2, y = y1 ++ y2.
INFER_LEN_SPLIT,
// length split empty, for example:
// z = "" V z != ""
// This is inferred when, e.g. x = y, x = z ++ x1, y = y1 ++ z
INFER_LEN_SPLIT_EMP,
// string split constant
// x = y, x = "c" ++ x2, y = y1 ++ y2, y1 != ""
// implies y1 = "c" ++ y1'
// This is a special case of F-Split in Figure 5 of Liang et al CAV 2014.
INFER_SSPLIT_CST,
// string split variable, for example:
// x = y, x = x1 ++ x2, y = y1 ++ y2
// implies x1 = y1 ++ x1' V y1 = x1 ++ y1'
// This is rule F-Split in Figure 5 of Liang et al CAV 2014.
INFER_SSPLIT_VAR,
// flat form loop, for example:
// x = y, x = x1 ++ z, y = z ++ y2
// implies z = u2 ++ u1, u in ( u1 ++ u2 )*, x1 = u2 ++ u, y2 = u ++ u1
// for fresh u, u1, u2.
// This is the rule F-Loop from Figure 5 of Liang et al CAV 2014.
INFER_FLOOP,
};
std::ostream& operator<<(std::ostream& out, Inference i);
/**
* Length status, used for indicating the length constraints for Skolems
* introduced by the theory of strings.
*/
enum LengthStatus
{
// The length of the Skolem should not be constrained. This should be
// used for Skolems whose length is already implied.
LENGTH_IGNORE,
// The length of the Skolem is not specified, and should be split on.
LENGTH_SPLIT,
// The length of the Skolem is exactly one.
LENGTH_ONE,
// The length of the Skolem is greater than or equal to one.
LENGTH_GEQ_ONE
};
/**
* This data structure encapsulates an inference for strings. This includes
* the form of the inference, as well as the side effects it generates.
*/
class InferInfo
{
public:
InferInfo();
/**
* The identifier for the inference, indicating the kind of reasoning used
* for this conclusion.
*/
Inference d_id;
/** The conclusion of the inference */
Node d_conc;
/**
* The antecedant(s) of the inference, interpreted conjunctively. These are
* literals that currently hold in the equality engine.
*/
std::vector<Node> d_ant;
/**
* The "new literal" antecedant(s) of the inference, interpreted
* conjunctively. These are literals that were needed to show the conclusion
* but do not currently hold in the equality engine.
*/
std::vector<Node> d_antn;
/**
* A list of new skolems introduced as a result of this inference. They
* are mapped to by a length status, indicating the length constraint that
* can be assumed for them.
*/
std::map<LengthStatus, std::vector<Node> > d_new_skolem;
/**
* The pending phase requirements, see InferenceManager::sendPhaseRequirement.
*/
std::map<Node, bool> d_pending_phase;
/**
* The index in the normal forms under which this inference is addressing.
* For example, if the inference is inferring x = y from |x|=|y| and
* w ++ x ++ ... = w ++ y ++ ...
* then d_index is 1, since x and y are at index 1 in these concat terms.
*/
unsigned d_index;
/**
* The normal form pair that is cached as a result of this inference.
*/
Node d_nf_pair[2];
/** for debugging
*
* The base pair of strings d_i/d_j that led to the inference, and whether
* (d_rev) we were processing the normal forms of these strings in reverse
* direction.
*/
Node d_i;
Node d_j;
bool d_rev;
};
} // namespace strings
} // namespace theory
} // namespace CVC4
#endif /* CVC4__THEORY__STRINGS__THEORY_STRINGS_H */
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